1. Field of the Invention
The invention generally relates to solid-state imaging devices and cameras. More particularly, the invention relates to a solid-state imaging device and a camera provided with the solid-state imaging device.
2. Description of the Related Art
Solid-state imaging devices are classified broadly into amplification type solid-state imaging devices, which are typically illustrated by CMOS (complementary metal-oxide semiconductor) image sensors, and charge transfer type imaging devices, which are typified by CCD (charge-coupled device) image sensors.
As to CMOS image sensors, the trend of replacement has been in progress at rapid speed particularly in the area of portable device-oriented image sensors from typical CCD sensors to the CMOS image sensors owning to high performance and low power consumption characteristics of the latter sensors. The CMOS image sensor is provided by including an imaging section having a plurality of pixels regularly arranged in a two-dimensional array, each of the pixels including a photodiode (PD) serving as a photoelectric conversion element and several pixel transistors; and peripheral circuits disposed around the imaging section.
The peripheral circuits include at least column circuits (so-called vertical driving units) for transmitting signals in the column direction, and horizontal circuits (so-called horizontal driving units) for sequentially transferring the signals, which are transmitted column wise by the column circuits, to an output circuit. The pixel transistors have a known configuration such as, for example, four-transistor circuit configuration including transfer, reset, amplifying, and selection transistors; or three-transistor circuit configuration including the transfer, reset, and amplifying transistors excepting the selection transistor.
The CMOS image sensor is generally provided by arranging a plurality of unit pixels, in which each of the unit pixels includes one photodiode and several pixel transistors, as a set. In recent years the miniaturization of the pixel size has been noticeable. With regard to the CMOS image sensor including a large number of pixels, many CMOS image sensors configured to share pixel transistors with a plurality of pixels in order to reduce the number of pixel transistors per unit pixel are known.
As the method of improving sensitivity while maintaining resolution without reducing the pixel size, the improvement of sensitivity by means of the slant arrangement of pixels is known. In addition, the improvement of luminosity signal sensitivity in the pixel is also known, which is carried out by employing a white pixel or alternatively a gray pixel (refer to Japanese Unexamined Patent Application Publication No. 2003-199117, Japanese Unexamined Patent Application Publication No. 2003-318375, Japanese Unexamined Patent Application Publication No. 2007-53731, and Japanese Unexamined Patent Application Publication No. 2002-135792). FIG. 1 schematically illustrates an image sensor including a white pixel, disclosed in Patent document 4. In this image sensor 102, as shown in FIG. 1, one unit is formed by including two pixels each vertically and horizontally, four pixels in total, a red pixel 101R, a green pixel 101G, a blue pixel 101B, and a white pixel 101W are disposed in the unit to form a pixel unit, and a number of the thus formed pixel unit structures are arranged two-dimensionally. Incidentally, it is noted on the slant arrangement of pixels that the vertical and horizontal resolutions can be retained, however the resolution in a slanting direction is decreased.